Organic polymeric materials such as plastics and resins and lubricating and mineral oil are subject to thermal, oxidative and photodegradation. A great variety of stabilizers are known in the art for stabilizing various substrates. Their effectiveness varies depending on the causes of degradation and the substrate stabilized. During the course of this work it was discovered that stabilizers that are very effective long term antioxidants are relatively poor process stabilizers which require stabilization of the substrate, against thermal degradation for a short time but at a relatively high temperature. Many stabilizers are relatively incompatible with the substrates which causes problems during the life of a product and lessens the stabilizer's effectiveness. Some stabilizers are either too volatile or thermally or hydrolytically unstable to be practical as commercial stabilizers.
The phosphonites of this invention possess an unusual combination of desirable properties as compared to the prior art phosphonites which makes these compounds particularly effective and useful as stabilizers. The prior art discloses unhindered 2,2'-biphenylenephenylphosphonite (J. Am.Chem.Soc.88, 168-9 (1966) and 2,2'-methylene bis(dialkylphenyl) phenylphosphonites (U.S. Pat. No. 3,297,631), the latter being said to inhibit oxidative degradation of polyolefins, especially polypropylene. However the phosphonites of this invention are much more effective, especially as process stabilizers of polyolefins and other substrates.